High speed drilling spindle with reciprocating ceramic shaft and edoubl-gripping centrifugal chuck

ABSTRACT

A spindle capable of operation at 200,000 revolutions per minute (RPM) with a reciprocating shaft design to minimize the moving mass. The spindle has a ceramic spindle shaft to decrease the moving mass and increase the shaft stiffness for better dynamic stability. The spindle employs a built-in linear motor to provide direct drilling motion to move the shaft along the axis, and a permanent magnet DC brushless motor to rotate the spindle shaft. The linear motor is coupled to the shaft by a combination of an air bearing and a magnetic thrust bearing to reduce the size of the thrust area for better dynamic stability and reduction in stresses of material. A double gripping centrifugal chuck is mounted in the hollow ceramic shaft, and reduces drill bit runout.

TECHNICAL FIELD OF THE INVENTION

This invention relates to high speed drilling systems for precisiondrilling of work pieces such as printed circuit boards and the like, andmore particularly to systems for drilling very small diameter holes insuch work pieces at high speed.

BACKGROUND OF THE INVENTION

Printed circuit boards are typically populated with many surface-mountedcircuit devices. Many small holes are formed in the boards tointerconnect the layers of the circuit board. Printed circuit boards arealso populated with other types of devices which also need holes formedin the boards.

Drilling machines are typically used to drill the holes in the printedcircuit boards. One exemplary type of system is described in U.S. Pat.No. 4,761,876, the entire contents of which are incorporated herein bythis reference.

There has been a dramatic increase in the hole count on printed circuitboards, which makes the cost of drilling the holes a significant part ofthe total production cost. In addition, hole sizes are getting smaller.Small drills are more expensive and can not be fed with the samevelocity as larger drills. Due to this fact, drilling time and cost arefurther increased.

To increase the throughput, higher drill bit rotation rates can beemployed. However, there is a limit on the spindle rotation rate, whichis due to the effect of the large centrifugal forces acting on thespindle rotors at very high rotation rates. Typically, the spindle isfabricated as a solid rod of steel, which will have a growth in therotor diameter due to centrifugal force at very high rotation rates.Because the rotor typically is supported on air bearings with relativelysmall gaps between the bearing structure and the rotor, the growth inthe rotor diameter will close or significantly narrow these bearinggaps, leading to seizure of the rotor in the bearings.

Drilling spindles typically use a chuck such as a centrifugal chuck togrip the drilling tool while it is being rotated. Centrifugal chucks areadvantageous since the tool can be changed without mechanicallyoperating a release mechanism, as there is no gripping centrifugal forcewhen the chuck is not rotated. Small drill applications can have verysmall drill bit runout tolerances, which can be difficult to achievewith centrifugal chucks in a single grip configuration.

It would therefore represent an advance in the art to provide a spindlecapable of extremely high drilling speeds.

It would also be an advantage to provide a centrifugal chuck capable ofgripping tools with significantly reduced run-out.

SUMMARY OF THE INVENTION

This invention provides many advantages and features. One aspect of theinvention is a spindle capable of operation at 200,000 revolutions perminute (RPM) with a reciprocating shaft design to minimize the movingmass. Another aspect of the invention is a double gripping centrifugalchuck for a drilling spindle to reduce drill bit run-outs.

In accordance with a further aspect of the invention, a combination ofan air bearing and a magnetic thrust bearing is employed to reduce thesize of the thrust area for better dynamic stability and reduction instresses of material.

A drilling spindle in accordance with another aspect of the inventionincludes a ceramic spindle shaft to decrease the moving mass andincrease the shaft stiffness for better dynamic stability. The spindleemploys a built-in linear motor to provide direct drilling motion, and apermanent magnet DC brushless motor to rotate the spindle shaft.

In one exemplary embodiment, a high speed drilling spindle in accordancewith the invention includes a spindle body, a rotatable rotor shaftsupported within the spindle body for high speed rotation about a rotoraxis. The rotor shaft is fabricated of a ceramic material capable ofwithstanding centrifugal forces exerted during high rotation rateswithout significant diametrical growth of the rotor shaft. A rotary airbearing supports the rotor shaft for high speed rotation with lowfrictional drag within the spindle body. A rotary drive system impartsrotational drive forces to the rotor shaft so as to rotate the shaft onthe rotary bearing at high speeds. A linear drive system imparts anaxially directed drive force to the rotor shaft to perform drillingmovements. A thrust bearing couples the linear drive system to the rotorshaft, and includes an air bearing and a magnetic thrust bearing.

The rotary drive system includes a DC brushless permanent magnet motor,with a permanent magnet mounted within an opening formed in the rotorshaft.

The spindle includes a centrifugal chuck mounted in the rotor shaft,holding a tool having a tool shank in place during high speed rotationto perform tool operations. The chuck is adapted to grip the drill shankat two separated points along the shank to guarantee parallelism of theshank to the axis of rotation. The chuck includes a uni-body flexurewhich has two gripping segments, the first gripping segment at a frontend of the chuck and the second gripping segment at a back end of thechuck. Each gripping segment includes a plurality of weights distributedabout the chuck axis and which are joined by flexures to form a uni-bodyconstruction.

BRIEF DESCRIPTION OF THE DRAWING

These and other features and advantages of the present invention willbecome more apparent from the following detailed description of anexemplary embodiment thereof, as illustrated in the accompanyingdrawings, in which:

FIG. 1A is a side cross-sectional view of a drilling spindle inaccordance with aspects of this invention.

FIG. 1B is a partial cross-sectional view of the spindle of FIG. 1A,rotated with respect to FIG. 1A and showing elements of the linear motorin further detail.

FIG. 2 is a schematic view illustrative of general magnetic elements ofthe motor providing the rotary drive for the drilling spindle of FIG. 1.

FIG. 3 is a functional block diagram of the spindle and the ancillarysystem elements for operating the spindle.

FIG. 4 is an isometric view of a centrifugal chuck comprising thespindle of FIG. 1 showing the forward end of the chuck.

FIG. 5 is an isometric, partially broken away view of the centrifugalchuck of FIG. 4.

FIG. 6 is an isometric view of the centrifugal chuck, showing the inwardend of the chuck.

FIG. 7 is a partially broken-away isometric view of the front end of thecentrifugal chuck.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The Spindle

FIG. 1 is a side cross-sectional view of an exemplary drilling spindle50 embodying aspects of the present invention. The spindle includes aspindle housing 52, which in an exemplary embodiment is stationary in arotational sense. The spindle 50 is typically mounted on an overheadbeam or gantry, in the manner illustrated in U.S. Pat. No. 4,761,876. Awork piece is positioned on a work table below the gantry, which ismoved relative to the spindle by an X-Y positioning system. In thisembodiment, the spindle is fixed in the X-Y sense, although in otherapplications, it can be moved in the X-Y as well as Z directions toprovide relative motion to position the spindle and the work piece andfor other functions such as tool changing.

A reciprocating spindle shaft 60 is mounted within the spindle body 52,and is rotatable, by a rotary drive system, and axially movable, by alinear drive system, to advance/retract the shaft along the spindle axis54. The shaft is shown in the advanced, down position in FIG. 1. Insteadof being fabricated of a steel, the shaft is fabricated of a materialwhich is very stiff and which has significantly less diametric growththan a steel shaft at high shaft revolution rates. In this exemplaryembodiment, the reciprocating shaft 60 is fabricated of a ceramicmaterial to obtain a shaft of high stiffness (high Young's modulus),relatively low weight, and low diametric growth at high revolutionrates. An exemplary ceramic material is the product UL 600 of CoorsCeramic Company, 600 Ninth Street, Golden, Colo. 80401, which isbelieved to be 96% alumina, with a Young's modulus value of 44 million,and which is fabricated to produce a sintered alumina ceramic tube. Incontrast, tool steel has a typical Young's modulus value on the order of30 million, and so the ceramic tube is much stiffer. Ceramic tubessuitable for the purpose can be fabricated by those skilled in theindustrial ceramics art.

In one exemplary embodiment, the shaft is a hollow tube having an outerdiameter of 0.7 inch, an inner diameter of 0.5 inch, and a length of 6inches. This tube has a typical weight of 0.3 pound, in contrast to anall metal shaft which could weigh 0.75 pounds or more. The shaft isreciprocated along the shaft axis in the spindle through a range of 0.4inch. A conventional spindle with a non-reciprocating shaft, requiringthe entire spindle to be moved up/down, can weight 12-20 pounds.

The shaft 60 is captured in two radial air bearings 70, 72. The firstair bearing 70 is at the front (distal) end 62 of the shaft. The secondair bearing 72 is at the back (interior) end 64 of the shaft. Airbearing 70 is supplied with pressurized air from an air supply connectedat port 74, through passageway 70A and transverse openings includingopenings 70B, 70C formed in the body and extending radially about theshaft opening. Air bearing 72 is supplied with pressurized air from anair supply connected at port 122, through passageway 72A and transverseopenings including openings 72B, 72C formed in the body and extendingradially about the shaft opening. The radial air bearings support theshaft 60 during rotation and also allow it to move up and down along therotating axis 54.

The ceramic shaft 60 is a hollow tubular shaft, with a hole 62 runningthrough its center. A centrifugal chuck 150 is mounted in a steel sleeve148 attached in the front end of the shaft within the hole 62. Thefunction of the sleeve is to distribute local stresses and preventfracturing of the ceramic shaft 60. The sleeve can be very lightlypressed into place within the hole 62, or preferably secured in place byepoxy. In accordance with an aspect of the invention, the shaft 60 issupported for rotation at rates which can exceed 200,000 revolutions perminute. The shaft is driven by a rotary drive system comprising a DCpermanent magnet brushless motor 80. In accordance with another aspectof the invention, the motor includes a rare earth permanent magnet 82mounted in the middle of the shaft 60 within the hole 62, and preferablysecured in place by epoxy. The permanent magnet DC motor 80 furtherincludes a stator circuit 84 mounted in the bore of the spindle housing52 between the radial air bearings 70, 72. The stator circuit 84includes a plurality of stator structures 84A each having a statorwinding 84B wound thereon. The magnet 82 has formed therein axiallyaligned north and south poles. A DC motor driver provides excitationsignals to the stator windings 84B, setting up electromagnetic fieldswhich act on the magnet 82, imparting a rotational force to the magnetand thus to the shaft.

FIG. 2 is a schematic view illustrative of general magnetic elements ofthe rotary drive motor 80. In this schematic end view, the north andsouth poles of the magnet 82 are represented as N and S, respectively.The stator lamination structures 84A and the windings 84B are depictedschematically. As shown therein, the magnet 82 is disposed within theopening in the hollow shaft tube. A metal sleeve (not shown) could beused to line the inside of the shaft tube in the region in which themagnet is positioned. This exemplary form of motor is a 2-pole, 3-phasemotor, although other types of electrical motors could alternatively beemployed.

It is noted that rare earth magnet DC brushless motors are generallyknown in the art, as well as techniques for driving the motors. Theplacement of the magnet within a hollow spindle shaft is not known. Athigh rotation rates, the magnet will tend to have diametrical growth dueto the high centrifugal forces exerted on the magnet during rotation. Ifthe magnet were to be placed on the external periphery of the shaft,this diametrical growth could lead to magnet damage or seizure of therotor. However, the ceramic shaft 60 is stiff enough to withstand thecentrifugal force without a significant diametrical expansion, and tohold the magnet within the shaft opening.

Again referring to FIG. 1A, a steel thrust plate 88 is attached at theback end of the shaft 60, e.g. by epoxy. The plate 88 defines a flange88A having a diameter larger than the outer diameter of the shaft 60.The purpose of the flange is to prevent the shaft 60 from sliding out ofthe spindle body. The flange 88A will contact the air bearing structureto provide a lower travel stop on the axial movement of the shaft.

The spindle 50 thus comprises a shaft assembly 90 with severalcomponents, including the hollow ceramic shaft 60, the centrifugal chuck150 for holding the drill bit, the permanent magnet 82 to providerotation to the shaft, and the thrust plate 88. The thrust plate 88accepts the Z-axis driving motion applied to the shaft 60 through athrust bearing 100 from the linear drive system 110. The thrust bearing100 includes a thrust bearing slider 104.

The thrust bearing 100 provides the combination of amagnetically-attracted and an air-pressure-repelled thrust bearing inthis embodiment to reduce the area required for the thrust bearing. Thisreduction in the thrust bearing area decreases the stress level in thethrust bearing flange 88A. The thrust plate 88 is attracted toward amagnet plate 102 installed in the forward end of the thrust bearingslider 104, and repelled at the same time by an air thrust bearing 106built into the magnet plate 102. Air pressure between the magnet plate102 and the thrust plate 88 creates a gap at interface 108 between thesetwo components and allows the shaft 62 to rotate in respect to thethrust bearing slider 104 which does not rotate. The magnet plate 102 isa permanent magnet structure. The air bearing 106 is supplied bypressurized air at port 122.

The thrust bearing slider 104 is captured in two radial air bearings104B, 104C which keep it in position and allow up and down reciprocatingmotion to drive the spindle shaft 60 and the drill bit into the workpiece. This motion is generated by the linear motor 110 attached to theback of the spindle.

The drive system 110 includes a linear motor comprising a motor coilstructure 112 formed in a cup-like configuration, with coil windings112A and 112B wound about the periphery of the cup-like structure, asshown in FIGS. 1A and 1B. in an exemplary embodiment, the coil structure112 is fabricated of aluminum, and is cooled by air. The thrust bearingslider 104 is attached to the coil structure 112 by fasteners 104A, andis provided with an anti-rotation device which is attached to the linearmotor coil 112, and interacts with the wall of linear motor adapter 114.The anti-rotation device is a pin 115 which slides in a slot 117 formedin the linear motor housing. A pair of TEFLON (TM) dowels is disposed oneither side of the pin within the slot to guide the pin in the slot. Thepin 115 extends from the coil structure which rides up/down within aslot formed in the adaptor housing.

A linear motor magnet assembly 116 is attached by a clamping device 118into the linear motor adapter 114, which is secured at the upper end ofthe spindle housing structure 52. The magnet assembly 116 includes aniron cylinder 116A, and iron core elements 116B, 116C supported insidethe cylinder 116A, which sandwich permanent magnets 116D and 116E. Themagnet assembly 116 is stationary, while the coil structure 112 movesaxially along axis 54 within a gap between the cylinder 116A and thesandwiched iron core elements 115 and magnets 116C in response to linearmotor drive signals applied to the coil windings. In this exemplaryembodiment, the linear motor provides an axial range of movement to theshaft of 0.4 inch, although other applications may require differentmovement ranges. The excitation drive signals to the linear motor areprovided on a set of leads 119 which are coupled to the linear motordriver.

Air to all air bearings is distributed to fittings at port 122. Coolingwater is also distributed through input fitting 124, into the spindlebody and output through output fitting 126, and is routed withinpassageways 128 within the spindle body around the air bearings end tothe DC permanent magnet brushless motor 80 to keep the spindle atconstant temperature.

FIG. 3 is a functional block diagram of the spindle 50 and the ancillarysystem elements for operating the spindle. These ancillary elementsinclude a controller/motor driver system 30 which generates the motordrive signals for the rotary drive motor 80 and for the linear drivemotor 110. A pressurized air supply 32 is connected to the spindlehousing to supply the air bearings. A recirculating coolant supply isalso connected to the spindle housing to circulate a liquid coolantthrough the spindle housing.

The Centrifugal Chuck

The centrifugal chuck 150 is illustrated in further detail in FIGS. 4-7.The centrifugal chuck 150 holds the drill bit 10 in place duringdrilling operations, and is designed to provide the capability to gripthe drill shank 12 at two points 152, 154 which are separated along theaxis of rotation of the tool shank. Engaging the shank at two pointsguarantees parallelism of the shank to the axis of rotation.

The chuck 150 is designed in the form of a uni-body flexure which hastwo gripping segments 160 and 170, the first 160 at the front and thesecond 170 at the back of the chuck 150. Each gripping segment includesfour weights which are joined by flexures to form a uni-bodyconstruction. Thus, the first gripping segment 160 includes four weights162A, 162B, 162C and 162D which are joined adjacent a gripping end byflexures 164A, 164B, 164C and 164D. The second gripping segment 170includes four weights 172A, 172B, 172C and 172D which are joined byflexures 174A, 174B, 174C and 174D. The joining flexures are disposedwell away from the longitudinal center of mass of the respectiveweights, permitting movement of the weights in a pivoting action inresponse to centrifugal forces.

The front and back gripping segments are connected with each other byfour thin wall flexures 180A, 180B, 180C and 180D. Each weight, whenexposed to the spindle rotation, is subjected to centrifugal force whichmoves it outward. It then rotates around a pivot point defined by a ringof metal protruding from the flexures joining the four weights of eachgripping segment, and rests against the interior sleeve 148 fitted intothe bore in the spindle shaft. During this motion the gripping end ofthe weight is closing on the shank 12 of the drill bit 10 to apply forceon the drill shaft to provide the drilling torque for the drill bit andto overcome drill bit resistance when entering the material. Thus, forexample, weight 162A has a weighted end 162A1 and a gripping end 162A2.The weighted end 162A1 moves outwardly in response to centrifugal force,pivoting about the ring 165 at flexures 164A, 164B to apply leverageforce to move gripping end 162A2 inwardly against the shank 12. The ringsurface protrudes slightly, by a few thousandths of an inch, from theexterior surface of the chuck. Similarly, exemplary weight 172C (FIG. 6)has a weighted end 172C1 and a gripping end 172C2. The weighted end172C1 moves outwardly in response to centrifugal force, pivoting aboutthe ring 175 flexures 174C, 174D to apply leverage force to movegripping end 172C2 inwardly against the shank 12. The other weightsoperate in a similar fashion.

The chuck is fabricated from a block of tool steel, which is machined toproduce the uni-body chuck structure.

A rubber O-ring 192 is installed into a groove 194 of the front segmentof the chuck to frictionally engage the shank 12, which keeps the drillbit in the centrifugal chuck when it is not rotating. The front ring 165has a slightly larger outer diameter (by, e.g., 1 inch) than the outerdiameter of the ring 175, and is pressed into the sleeve 148. The backsegment of the chuck, at ring 175, has a slip fit into the sleeve 148 toallow it to float in the bore when actuated. Behind the chuck 150 is adisk 200 with a threaded hole in the center which allows chuck removalwithout damage.

The front segment 160 of the chuck 150 is pressed into the sleeve in thespindle shaft and the bore of the chuck is ground on the assembly toguarantee concentricity of the drill shank with the axis of rotation.The front of the chuck is secured by a wire ring 196 (FIG. 1) located ina groove 198, which prevents the chuck from being forced out of thespindle nose.

The chuck can be removed from the rotor shaft by inserting a threadedshaft into the chuck and threading it into the chuck removal disk andthen applying force outwardly to the shaft. The disk in that conditionis applying force to the chuck and forces it out of the bore of thespindle shaft.

The grip on the drill shank is increasing with the increase of the rpmand it is strongest on the highest rpm. The grip on the drill shank isadequate to be able to rout with 0.062 diameter router in a three highstack of boards each 0.062 thick.

It is understood that the above-described embodiments are merelyillustrative of the possible specific embodiments which may representprinciples of the present invention. Other arrangements may readily bedevised in accordance with these principles by those skilled in the artwithout departing from the scope and spirit of the invention.

What is claimed is:
 1. A high speed drilling spindle for a drillingsystem, comprising:a spindle body; a rotatable rotor shaft supportedwithin the spindle body for high speed rotation about a rotor axis, saidrotor shaft fabricated of a ceramic material capable of withstandingcentrifugal forces exerted during high rotation rates withoutsignificant diametrical growth of the rotor shaft; a rotary bearing forsupporting the rotor shaft for high speed rotation with low frictionaldrag within the spindle body; and a rotary drive system for impartingrotational drive forces to the rotor shaft so as to rotate the shaft onthe rotary bearing at high speeds.
 2. The spindle of claim 1 furthercomprising a linear drive system for imparting an axially directed driveforce to the rotor shaft to perform drilling movements.
 3. The spindleof claim 1 wherein said rotary drive system includes a DC brushlesspermanent magnet motor, said motor comprising a stator assemblyincluding a plurality of stator windings, said stator assembly mountedwithin said spindle body, and a permanent magnet mounted within anopening formed in said rotor shaft, the magnet having axially extendingnorth and south magnetic poles which are acted upon by magnetic fieldsestablished as a result of excitation signals applied to the statorwindings to impart rotational forces to the rotor shaft.
 4. The spindleof claim 1 wherein said high rotation rates include 200,000 revolutionsper minute.
 5. The spindle of claim 1 wherein said rotor shaft includesa hollow tubular structure fabricated of said ceramic material.
 6. Thespindle of claim 5 wherein said rotary drive system includes a magnetdisposed within said hollow tubular structure.
 7. The spindle of claim 5wherein said hollow tubular structure has an outer diameter of 0.7 inch,and an inner diameter of 0.5 inch.
 8. A high speed drilling spindlecomprising:a spindle body; a rotatable rotor shaft supported within thespindle body for high speed rotation about a rotor axis, said rotorshaft fabricated of a ceramic material capable of withstandingcentrifugal forces exerted during high rotation rates withoutsignificant diametrical growth of the rotor shaft; a rotary bearing forsupporting the rotor shaft for high speed rotation with low frictionaldrag within the spindle body; a rotary drive system for impartingrotational drive forces to the rotor shaft so as to rotate the shaft onthe rotary bearing at high speeds; a linear drive system for impartingaxially directed drive forces to the rotor shaft to reciprocate therotor shaft along a shaft axis, the linear drive system including alinear motor and a magnetically attracted and air-bearing-repelledthrust bearing for coupling the linear drive system to the rotor shaft,said thrust bearing including an air bearing; and a centrifugal chuckfor holding a tool mounted in a distal end of the ceramic shaft.
 9. Thespindle of claim 8 wherein the thrust bearing comprises a thrust plateattached at an interior end of the shaft, said linear drive systemcomprises a magnet attached to a thrust bearing slider structure andpositioned adjacent said thrust plate, wherein said magnet and saidthrust plate are magnetically attracted to each other, and said thrustair bearing repels said magnetic attraction to prevent said magnet andsaid thrust plate from coming into contact.
 10. The spindle of claim 8wherein said linear drive system includes a linear drive motor, saidlinear drive motor comprising an axially movable coil structure havingcoil windings disposed about the coil structure, a linear motor magnetassembly having core elements fabricated of a magnetic material and oneor more permanent magnets, said magnet assembly being stationary withrespect to the spindle housing, said coil structure moving axially inresponse to linear motor drive signals applied to the coil windings. 11.The spindle of claim 10 wherein said coil structure is a cylindricalcupped structure having an open end and a closed end, said coil windingsdisposed about a periphery of said cupped structure.
 12. The spindle ofclaim 8 herein said shaft comprises a hollow ceramic tube structure, andsaid chuck is disposed within a sleeve member inserted into said distalend of said ceramic shaft, said sleeve member fabricated of a metalmaterial to relieve localized stresses exerted by the chuck on theceramic shaft.
 13. The spindle of claim 8 wherein said rotary drivesystem includes a DC brushless permanent magnet motor, said motorcomprising a stator assembly including a plurality of stator windings,said stator assembly mounted within said spindle body, and a permanentmagnet mounted within an opening formed in said rotor shaft, the magnethaving axially extending north and south magnetic poles which are actedupon by magnetic fields established as a result of excitation signalsapplied to the stator windings to impart rotational forces to the rotorshaft.
 14. The spindle of claim 13 wherein the rotor shaft is a hollowceramic tube having a central opening formed therethrough, and saidpermanent magnet is disposed within said hollow opening.
 15. The spindleof claim 8 wherein said high rotation rates include 200,000 revolutionsper minute.
 16. The spindle of claim 8 wherein said rotor shaft includesa hollow tubular structure fabricated of said ceramic material.
 17. Thespindle of claim 16 wherein said rotary drive system includes a magnetdisposed within said hollow tubular structure.
 18. The spindle of claim16 wherein said hollow tubular structure has an outer diameter of 0.7inch, and an inner diameter of 0.5 inch.
 19. A centrifugal chuck for usein a spindle, holding a tool having a tool shank in place during highspeed rotation to perform tool operations, the chuck adapted to grip thedrill shank during rotation at first and second separated points alongthe shank to guarantee parallelism of the shank to the axis of rotation,the chuck comprising a uni-body flexure which has two gripping segments,the first gripping segment at a front end of the chuck and the secondgripping segment at a back end of the chuck, each gripping segmentincluding a plurality of weights distributed about the chuck axis andwhich are joined by flexures to form a uni-body construction.
 20. Thechuck of claim 19 wherein said plurality of weights for said firstgripping segment consists of four weights segments joined adjacent afirst gripping end of the chuck by a first set of correspondingflexures, and said plurality of weights for said second gripping segmentincludes four weights segments joined adjacent a second gripping end bya second set of corresponding flexures.
 21. The chuck of claim 19wherein said joining flexures are disposed well away from thelongitudinal center of mass of the respective weights, permittingmovement of the weights in a pivoting action in response to centrifugalforces.
 22. The chuck of claim 19 wherein the front and back grippingsegments are connected with each other by a plurality of thin wallflexures.
 23. The chuck of claim 19 wherein each of said weightsincludes a gripping end, and each of said two gripping segments includesa pivot ring protruding from the flexures joining the plurality ofweights, and each of said plurality of weights, when exposed to thespindle rotation, is subjected to centrifugal force which moves itoutward, rotating around the pivot ring, and during this motion thegripping end of the weight is pivoted inwardly, closing on a tool shankto apply force on the tool shank.
 24. The chuck of claim 23 wherein thepivot ring has an outer surface protruding slightly from an exteriorsurface of the chuck.
 25. The chuck of claim 19 further including acompressive element installed into a groove formed in the uni-body chuckto frictionally engage the shank and retain the tool in the centrifugalchuck when it is not rotating.
 26. The chuck of claim 23 wherein thepivot ring of the first gripping segment has a slightly larger outerdiameter than a corresponding outer diameter of the gripping ring of thesecond gripping segment.
 27. A high speed drilling spindle for adrilling system, comprising:a spindle body; a rotatable rotor shaftsupported within the spindle body for high speed rotation about a rotoraxis, said rotor shaft fabricated of a ceramic material capable ofwithstanding centrifugal forces exerted during high rotation rateswithout significant diametrical growth of the rotor shaft; a rotarybearing for supporting the rotor shaft for high speed rotation with lowfrictional drag within the spindle body; a rotary drive system forimparting rotational drive forces to the rotor shaft so as to rotate theshaft on the rotary bearing at high speeds; a linear drive system forimparting an axially directed drive force to the rotor shaft to performdrilling movements; and a thrust bearing for coupling the linear drivesystem to the rotor shaft, said thrust bearing including an air bearingand magnetically-attracted thrust surfaces.
 28. The spindle of claim 27wherein the magnetically-attracted thrust surfaces comprise a thrustplate attached at an interior end of the shaft and a magnet attached toa thrust bearing slider structure and positioned adjacent said thrustplate, wherein said magnet and said thrust plate are magneticallyattracted to each other, and said air bearing repels said magneticattraction to prevent said magnet and said thrust plate from coming intocontact.
 29. A high speed drilling spindle for a drilling system,comprising:a spindle body; a rotatable rotor shaft supported within thespindle body for high speed rotation about a rotor axis, said rotorshaft fabricated of a ceramic material capable of withstandingcentrifugal forces exerted during high rotation rates withoutsignificant diametrical growth of the rotor shaft; a rotary bearing forsupporting the rotor shaft for high speed rotation with low frictionaldrag within the spindle body; a rotary drive system for impartingrotational drive forces to the rotor shaft so as to rotate the shaft onthe rotary bearing at high speeds; a chuck for holding a tool mounted ina distal end of said ceramic shaft; and wherein said shaft comprises ahollow ceramic tube structure, and said chuck is disposed within asleeve member inserted into said distal end of said ceramic shaft, saidsleeve member fabricated of a metal material to relieve localizedstresses exerted by the chuck on the ceramic shaft.
 30. A high speeddrilling spindle for a drilling system, comprising:a spindle body; arotatable rotor shaft supported within the spindle body for high speedrotation about a rotor axis, said rotor shaft a hollow tube having acentral opening formed therethrough and fabricated of a ceramic materialcapable of withstanding centrifugal forces exerted during high rotationrates without significant diametrical growth of the rotor shaft; arotary bearing for supporting the rotor shaft for high speed rotationwith low frictional drag within the spindle body; and a rotary drivesystem for imparting rotational drive forces to the rotor shaft so as torotate the shaft on the rotary bearing at high speeds, said rotary drivesystem including a DC brushless permanent magnet motor, said motorcomprising a stator assembly including a plurality of stator windings,said stator assembly mounted within said spindle body, and a permanentmagnet mounted within said tube central opening, the magnet havingaxially extending north and south magnetic poles which are acted upon bymagnetic fields established as a result of excitation signals applied tothe stator windings to impart rotational forces to the rotor shaft. 31.A high speed drilling spindle for a drilling system, comprising:aspindle body; a rotatable rotor shaft supported within the spindle bodyfor high speed rotation about a rotor axis, said rotor shaft fabricatedof a ceramic material capable of withstanding centrifugal forces exertedduring high rotation rates without significant diametrical growth of therotor shaft; a rotary bearing for supporting the rotor shaft for highspeed rotation with low frictional drag within the spindle body; arotary drive system for imparting rotational drive forces to the rotorshaft so as to rotate the shaft on the rotary bearing at high speeds;and a linear drive system for imparting an axially directed drive forceto the rotor shaft to perform drilling movements, said linear drivesystem including a linear drive motor, a thrust bearing slider structureand a thrust bearing for coupling the thrust bearing slider structure tothe rotor shaft, said linear motor drive comprising an axially movablecoil structure having coil windings disposed about the coil structure, alinear motor magnet assembly having core elements fabricated of amagnetic material and one or more permanent magnets, said magnetassembly being stationary with respect to the spindle housing, said coilstructure moving axially in response to linear motor drive signalsapplied to the coil windings.
 32. The spindle of claim 31 wherein saidcoil structure is a cylindrical cupped structure having an open end anda closed end, said coil windings disposed about a periphery of saidcupped structure.
 33. The spindle of claim 32 wherein said linear motormagnet assembly is supported within said open end of said cuppedstructure.
 34. The spindle of claim 1 further comprising a chuck forholding a tool mounted in a distal end of said ceramic shaft.